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Predicting an Epidemic

Predicting an Epidemic. A Quantitative Assessment of TSE Sampling Data to Predict Outbreak Magnitude Aspen Shackleford HONR299J. Variant Creutzfeldt-Jakob Disease (vCJD). Linked to BSE Unknown number of individuals who may be infected Iatrogenic contamination.

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Predicting an Epidemic

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  1. Predicting an Epidemic A Quantitative Assessment of TSE Sampling Data to Predict Outbreak Magnitude Aspen Shackleford HONR299J

  2. Variant Creutzfeldt-Jakob Disease (vCJD) • Linked to BSE • Unknown number of individuals who may be infected • Iatrogenic contamination The National CJD Research & Surveillance Unit. (2014). Variant Creutzfeldt-Jakob Disease current data (March 2014) [Data file]. Retrieved from http://www.cjd.ed.ac.uk/documents/worldfigs.pdf

  3. How are outbreak predictions made? • Reporting • Statistical Models

  4. Dealler & Kent, 1995 • Age of onset of clinical BSE symptoms was sampled • Results • Decrease in peak age of onset • Led to further investigation of under-reporting Dealler, S.F. & Kent, J.T. (1995). BSE: an update on the statistical evidence. British Food Journal, 97 (8), 3-18. http://docserver.ingentaconnect.com

  5. Under-Reporting • MAFF Requirements • 2 visits by a veterinarian • Slaughter and send in tissue sample • Case denial • Dealler and Kent Suspicion • Paul Brown’s predictions • Farmer Initiative

  6. Paul Brown’s Prediction Brown, Paul. (2004). Mad Cow Disease in cattle and human beings: Bovine spongiform encephalopathy provides a case study in how to manage risks while still learning facts. American Scientist, 92 (4), 334-341. http://www.jstor.org/stable/27858422

  7. Under-Reporting • MAFF Requirements • 2 visits by a veterinarian • Slaughter and send in tissue sample • Case denial • Dealler and Kent Suspicion • Paul Brown’s predictions • Farmer Initiative

  8. Dealler and Kent Statistical Model (1995) • Based upon data collection year (i) and bovine age (j) • Follows a Poisson Distribution • Predicts the expected number of deaths at age j in year i from 1984 to 2001 • Reporting effect and parameters compensated for under-reporting

  9. Poisson Distribution • Requirements • Used to determine the frequency of an abnormal event • Graphical representation • r-curve closer to zero signifies a rare event The Warring States Project. (2007, August 24). Statistics: The Poisson distribution. Retrieved from http://www.umass.edu/wsp/resources/poisson/index.html

  10. Dealler and Kent Statistical Model (1995) • Based upon data collection year and bovine age • Follows a Poisson Distribution • Predicts the expected number of deaths at age j in year i from 1984 to 2001 • Reporting effect and parameters compensated for under-reporting

  11. Results • Model predictions from 1984 through 2001 (solid line) • Actual reports from 1984 to 1993 (dotted line) • Under-reporting • Peak in 1994 • Overlap Dealler, S.F. & Kent, J.T. (1995). BSE: an update on the statistical evidence. British Food Journal, 97 (8), 3-18. http://docserver.ingentaconnect.com

  12. Hagenaars et al., 2006 • Scrapie • Within-flock model • Sheep age • Genotypes: ARR (0.45), ARQ (0.5), VRQ (0.05) • Between-flock model • Model determines duration and magnitude of an outbreak

  13. N - flock-size • n - geometric mean of the size distribution • c1 , c2 – constants Hagenaars, T.J, Donnelly, C.A., & Ferguson, N.M. (2006). Epidemiological analysis of data for scrapie in Great Britain. Epidemiology and Infection, 134 (2), 359-367. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870388/

  14. Within Flock Results • Large case rate • Case rate less than 5 per year • Average number of cases: 2.8 per year Hagenaars, T.J, Donnelly, C.A., & Ferguson, N.M. (2006). Epidemiological analysis of data for scrapie in Great Britain. Epidemiology and Infection, 134 (2), 359-367. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870388/

  15. γ – the rate of recovery of affected farms • λ - the rate per capita that a farm becomes affected • t - time (in years) • at>0 - the number of sheep flocks that have experienced at least one BSE case since the starting year Hagenaars, T.J, Donnelly, C.A., & Ferguson, N.M. (2006). Epidemiological analysis of data for scrapie in Great Britain. Epidemiology and Infection, 134 (2), 359-367. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870388/

  16. Between Flock Results • Low basic reproduction rate • High basic reproduction rate • Breeding for resistance • ARR/ARR genotype • Changes in management Hagenaars, T.J, Donnelly, C.A., & Ferguson, N.M. (2006). Epidemiological analysis of data for scrapie in Great Britain. Epidemiology and Infection, 134 (2), 359-367. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870388/

  17. Conclusion • Statistical models are widely used • Statistical models offer information that uses parameters and constraints that model real life • The predictions of statistical models can be used to make decisions about how to best prevent an outbreak that threatens human and animal populations

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